1. Field of the Invention
The present invention relates to a method for producing of electronic integrated circuit, and more particularly to a method for self-assembling chips onto a substrate.
2. Description of Related Art
In general, an integrated circuit is composed of multiple electronic components on a single substrate so that the integrated circuit is high density and multi-functional. However, as the need for minimization and multi-function of electronic products, the quantity of electronic components on the integrated circuit relatively increases and the size of the electronic components is required to be smaller.
Take a light emitting diode (LED), which is a component made by semiconductor material, as an example. In general, the LED is a miniature, solid type light-emitting source and is able to transform electrical energy into light. Because of its features of long life time, good shock-proof ability, low drive voltage and mercury free, the LED could meet the needs of being light, thin, short and small for electronic industry nowadays. The LED is popular in various fields of daily life, e.g. car lamps, indicators, traffic signals and all kinds of consumer's products. Besides, since the popularization of LED and the features thereof, it is regarded as the new lighting device of 21st century recently.
The conventional LED could be divided into a lamp type and a surface mount type according to its type of packaging. Either type requires a pick-and-place device to move these chips onto a substrate or a metal bracket for packaging. However, when the size of the chip is smaller than 1 mm, the pick-and-place device is not going to fulfill the designed goal, even though these chips are attached by flip-chip method. Vacuum, static or airflow etc. is introduced to hold the chip smaller than 1 mm, but because these chips are so small that the pick-and-place processing is too time consuming and cost ineffective. Besides, the used equipment of above mentioned pick-and-place technique is very expensive, so it increases the difficulty and cost.
U.S. Pat. No. 5,355,577 disclosed a method using electrostatic force and shape complementary to self-assemble microstructures. However, the high voltage required during the process to provide sufficient electrical field increases safety concerns and cost of manufacture so it is difficult to be used.
Heiko O. Jacobs et. al. (Science, 296(12), 323-325 (2002)) disclosed a method to self-assemble a large quantity of microstructures onto a substrate of curved surface. The method applies the low-melting point solder which has a melting point around 50° C. to allow the microstructures to self-assemble and further remove the erroneous assembly by a disturbance to correct the assembly. However, the low melting point solder used by Jacobs et. al. is a unique material and difficult to obtain, which largely limits the practical application of the method.
U.S. Pat. No. 5,824,186 disclosed a different self-assembly method of microstructures. With reference to FIG. 1, according to the self-assembly method of microstructures disclosed by the patent a microstructure 100 of a predetermined shape is disturbed so as to move close to a substrate 102, which results in that the microstructure 100 is imbedded in a recess 104 which is predetermined in a surface of the substrate 102. It means that the recess 104 has the shape complementary to the microstructure 100. Moreover, alloy layer 106 with the low-melting point is formed on the interface of the microstructure 100 and the recess 104 to further allow the microstructure 100 to be adhered and positioned in the recesses 104 on the substrate 102. However, due to the limitations of having the recess 104 on the substrate 102 and having a shape complementary of each recess 104 to the microstructure 100, hence it increases the manufacture cost.
The self-assembling process includes the release of the microstructures and self assembling. After the release, the microstructures were randomly suspended in the liquid. The self assembling can occur because the shape of the microstructures is complementary to that of each recess or the property of the microstructures is different from that of the recess. However, the multi-bonding in the self assembling process is usually not so accurately because the microstructures fell in different directions, and if the shape or the properties cannot be matched, the self assembling cannot be achieved.
U.S. Pat. No. 5,545,291 disclosed a method for assembling microstructures onto a substrate through fluid transport. With reference to FIG. 11, silicon substrate 50 comprises etched recessed regions 55. A variety of techniques including wet etching, plasma etching, reactive ion etching, ion milling, among others provide recessed regions 50, or generally trenches, receptors, or binding sites. Such techniques etch recessed regions 50 with a geometric profile which is complementary to GaAs block 19. In the silicon substrate, for example, each recessed region includes a trapezoidal profile or inverted truncated pyramid shape. The trapezoidal profile allows GaAs block 19 to self-align and fit closely into recessed region 50 via the fluid transferring technique. Because the GaAs blocks 19 are randomly distributed in the liquid, the amount of the recessed regions 55 should be several times of that of the GaAs blocks 19 for good self assembling.
U.S. Pat. Nos. 6,527,964 and 6,623,579 disclosed a method and an apparatus for fluidic self assembly by disturbing and controlling the fluid flow. Furthermore, U.S. Pat. No. 6,780,696 disclosed a method and an apparatus for self-assembly of functional blocks on a substrate facilitated by electrode pairs.
However, in the prior art mentioned above, a large amount of the chips randomly distributed in the fluid was required, and the self assembling or the electric field attraction is required to be repeated for many times. Therefore, the steps of the self assembling process are increased, and thereby the manufacturing cost is increased and the design becomes more difficult.
Other objects, advantages and novel features of the invention will become more obvious from the following detailed description when taken in conjunction with the accompanying drawings.